Recently, various types of mobile radio communication systems have been developed and put into practical use with the development of the radio communication technique and an increase in the communication need, and a cellular radio communication system is provided as one example. FIG. 1 shows the schematic construction of the system. For example, the system includes a control station CS connected to a wire communication network NW via a circuit line CL.sub.0, a plurality of base stations BS.sub.1, BS.sub.2, BS.sub.3, . . . connected to the control station CS via respective circuit lines CL.sub.1 to CL.sub.n, and a plurality of mobile stations or units MU.sub.1, MU.sub.2, MU.sub.3, MU.sub.4, . . . . The base stations BS.sub.1, BS.sub.2, BS.sub.3 . . . respectively provide radio zones E.sub.1, E.sub.2, E.sub.3 . . . which are called cells for respective small different areas in the service area. Each of the mobile stations MU.sub.1, MU.sub.2, MU.sub.3, MU.sub.4, . . . is connected to the base station of the cell in which the mobile station lies via a corresponding radio channel and each of the mobile stations is connected to the wire communication network NW from the corresponding base station via the control station CS.
Recently, in the above system, an authentication procedure for the mobile station has been provided in the procedure for radio connection between the mobile station and the base station at the time of call originating, call incoming or registration of position. FIGS. 2 and 3 show an example of a sequence of originating call control procedures containing the authentication procedure.
Assume now that the user has effected the originating call operation in the mobile station as shown in FIG. 2. The mobile station generates an originating call signal containing a telephone number MIN (Mobile Identification Number) as a preset identification number of the mobile station and an authentication parameter corresponding to the MIN and transmits the originating call signal to the base station. For example, a count value indicating the number of communications using the MIN is used as the authentication parameter. The count value is counted up in the mobile station and base station each time the communication using the MIN is effected. Therefore, the count value of the mobile station and the count value of the base station for the same MIN are always equal to each other.
When the base station receives an originating call signal from the mobile station, it extracts the count value and MIN contained in the originating call signal and transfers a count value corresponding to the MIN held in the base station together with the extracted MIN and count value to the authentication management center. For example, the authentication management center is located in a control station of higher rank than the control station CS or a control station provided for a plurality of carriers.
The authentication management center first determines whether the received MIN is registered or not, and if the MIN is registered, it collates the count value with a count value for the same MIN counted in the base station. Then, if the collated count values are coincident with each other, it transmits a notice of authentication to the base station. When the base station receives the notice of authentication, it generates a channel specifying message and transmits the same to the mobile station and then seizes and registers a radio channel. When the mobile station receives the channel specifying message, it seizes a radio channel according to the channel specifying message. Thus, the radio link is created by the radio channel between the mobile station and the base station (connection of the radio channel).
On the other hand, if it is determined as the result of collation of the count value of the MIN in the authentication management center that the received count value does not coincide with the count value counted in the base station, the notice of authentication is not returned to the base station from the authentication management center. Therefore, if the notice of authentication is not returned after a preset time has passed after the base station has transmitted the MIN and count value to the authentication management center, the base station cancels the originating call as shown in FIG. 3 and does not issue a channel specifying message. Therefore, no radio link is created between the mobile station and the base station.
FIG. 4 shows a sequence in a case where an incoming call message from the base station is received. When the incoming call message is received from the base station, the mobile station transmits an incoming call signal containing its own MIN and a count value corresponding to the MIN to the base station. When the base station receives the incoming call signal, it extracts the MIN and count value contained in the incoming call signal and transfers them to the authentication management center. The authentication management center confirms that the received MIN is registered and then collates the count value in the same manner as in the case of originating call operation described before. Then, if the count values are coincident with each other, it transmits a notice of authentication to the base station. When the base station receives the notice of authentication, it generates and transmits a channel specifying message to the mobile station.
Thus, by providing the authentication procedure in the radio connection procedure, it becomes possible to prevent a dishonest act that a dishonest man makes a fraudulent use of another's MIN in his mobile station device to make communication with the charges put not on him but on the other person.
However, the conventional mobile station device having the radio connection function containing the authentication procedure has the following problem to be solved. That is, in the mobile station device, a RAM area called a NAM (Number Assignment Module) for storing MINs is provided to make a contract with a plurality of mobile communication corporations (carriers) and MINs can be freely set and reset by the user. When the mobile station is used, a MIN corresponding to the carrier is set by the user's operation to make ready for communication. However, a count value used as the authentication parameter is stored in a RAM different from the NAM and only a single count value is stored in the RAM. When the MIN is changed, the count value is reset.
Therefore, the count value cannot be adequately used when the MIN is changed. If the count value is changed at the time of change of MIN, the original state cannot be restored when the MIN is set to the original value again.